1. Field of the Invention
The invention relates to a lift axle suspension. In one of its aspects, the invention relates to a lift axle suspension with a compressed air reservoir for use in raising the lift axle suspension.
2. Description of the Related Art
In trailers or semi-tractors and other heavy-duty vehicles, it is common to use a lift axle suspension to accommodate the different loading scenarios of the tractor/trailer. The lift axle suspension is typically retained in a retracted position beneath the frame of the vehicle until it is needed. The lift axle suspension is lowered into contact with the ground to provide another suspension over which the load of the vehicle is distributed.
Lift axle suspensions typically comprise trailing arms on opposite sides of the vehicle that support an axle. Each trailing arm has one end pivotally mounted to a frame by a hanger bracket and another end connected to the frame by an air spring having an air bag that dampens the rotational movement of the trailing arm in response to forces transferred from the axle. The lift axle suspension further includes an air-operated lift bag for raising and lowering the lift axle suspension into and out of contact with the ground.
The wheels of a lift axle suspension are typically mounted to the axle so that there is a positive castor angle to ensure that the wheels will self-steer to follow the direction of the trailer when the trailer is moving forward. The positive castor angle precludes self-steering of the wheels when the trailer is driven in a rearward direction. The most common solution to the failure of the wheels to self-steer when the vehicle is backed up is to lift the suspension out of ground engaging contact.
The pressurized air for supplying air to the lift bags to lift the suspension during backing is provided by a primary compressed air tank found on the semi tractor. The primary air tank is filled with compressed air by a compressor on the semi tractor and is coupled to the lift bag and air bag systems through a pressure protection valve. The pressure protection valve also couples the primary tank to the vehicle brake system, which is also run on compressed air. The pressure protection valve is designed to shut off the flow of pressurized air to the air spring and lift spring systems when the pressure in the primary tank drops below a predetermined value to ensure sufficient air for the braking operations of the vehicle.
As part of the loading and unloading procedure, it is common to alternate between driving forward and backing up toward a dock to properly position the vehicle. If the lift suspension is activated, the lift bags are inflated and the ride air bags are exhausted to raise the suspension during each back movement and the lift bags are exhausted and the ride air bags inflated during each forward movement. Given the relative air volume of the lift bags and ride air bags and the capacity of the primary tank, the pressure in the primary tank can drop below the protection cut off limit, preventing the direction of compressed air to the lift bags for subsequent maneuvering until the pressure in the primary tank can be brought above the protection limit. Pressurization of the primary tank can take several minutes and can be required after a single backing. Needless to say, waiting any amount of time, let alone up to several minutes, for the primary tank to pressurize above the operational limit is considered a great disadvantage and an annoyance by the vehicle operator.
Previous attempts to address this solution have focused on adding secondary tanks to the vehicle, which are filled by the tractor compressor. The disadvantage of secondary tanks is that they are typically located within the frame of a tractor or trailer. Unfortunately, the typical tractor/trailer does not have the available space needed to properly locate and position a suitably sized secondary tank. Further, these auxiliary tanks add additional weight to the vehicle.
The invention relates to an improved trailing arm suspension alone or in combination with a vehicle having a pneumatic system and a vehicle frame on an axle with ground engaging wheels. The trailing arm suspension comprises a pair of trailing arm assemblies adapted to be mounted to the vehicle frame in spaced relationship. Each of the trailing arm assemblies comprises a trailing arm having one portion adapted to be pivotally mounted to the vehicle frame for pivotal movement about a pivot axis and a spring adapted to operably connect the trailing arm to the vehicle frame for resisting the pivotal movement of the trailing arm about the pivotal axis toward the frame. The axle is carried by the trailing arms and connected thereto for movement with the trailing arms. The spring is adapted to be coupled to the pneumatic air system to supply pressurized air thereto. A pneumatic lift mechanism is mounted on the trailing arm for raising the trailing arm with respect to the frame when pressurized. According to the invention, at least a portion of the axle has a sealed hollow interior forming a pressurized air reservoir and is pneumatically connected to the pneumatic lift mechanism for selectively raising the trailing arm with respect to the frame.
Preferably, the pneumatic lift mechanism is also pneumatically connected to one of the frame and the axle. The pneumatic lift mechanism is preferably an inflatable bag. The suspension can also include an air spring operably connecting the trailing arm to the frame and an air controller fluidly coupling the reservoir to the air spring and controlling the introduction of pressurized air from the reservoir to the air spring.
The axle can be made in various ways but preferably comprises an enclosed and sealed elongated hollow; body forming the air reservoir. The hollow body comprises an elongated plate with a u-shaped cross section defining an open top and open ends, a top plate mounted to the u-shaped plate to cover the open top, and end plates mounted to the u-shaped plate to cover the open ends. The axle can include a spindle assembly mounted to each end of the hollow body for rotatably mounting ground engaging wheels. The spindles are typically rotatably mounted to the axle to form a steerable axle.
A valve can be provided in a pneumatic line between the air reservoir and the pneumatic lift mechanism for controlling the pneumatic pressure to the pneumatic lift mechanism. A controller can be connected to the valve for selectively controlling the operation of the valve. A direction sensor can be provided and electrically or pneumatically coupled to the controller for detecting a reverse operation of the vehicle and to open the valve and raise the trailing arm when the vehicle moves in a reverse direction. The direction sensor can also detect a forward operation of the vehicle to exhaust the pressurized air from the pneumatic lift mechanism during forward operation to lower the trailing arm with respect to the frame. Preferably, the direction sensor is a back-up light circuit for the vehicle or a transmission switch.
Further according to the invention, an improved trailing arm suspension for supporting a vehicle with a pneumatic system between a vehicle frame and an axle with ground engaging wheels comprises a pair of trailing arm assemblies adapted to be mounted to the vehicle frame in spaced relationship. Each of the trailing arm assemblies comprises a trailing arm having one portion adapted to be pivotally mounted to the vehicle frame for pivotal movement about a pivot axis and a spring adapted to operably connect the trailing arm to the vehicle frame for resisting the pivotal movement of the trailing arm about the pivotal axis toward the frame and adapted to be coupled to the pneumatic air system to supply pressurized air thereto. At least a portion of the axle has a hollow interior forming a pressurized air reservoir and is connected to the pneumatic system. According to the invention, a pneumatic lift mechanism is connected to the trailing arm for raising the trailing arm with respect to the frame when pressurized with air and the pneumatic lift mechanism is connected to the air reservoir for selectively raising the trailing arm with respect to the frame.
Still further according to the invention, an improved trailing arm suspension for supporting a vehicle with a pneumatic system between a vehicle frame and an axle with ground engaging wheels comprises a pair of spaced apart trailing arm assemblies adapted to be mounted to the vehicle frame. Each of the trailing arm assemblies comprises a trailing arm having one portion adapted to be pivotally mounted to the vehicle frame for pivotal movement about a pivot axis and an air spring adapted to operably connect the trailing arm to the vehicle frame for resisting the pivotal movement of the trailing arm about the pivotal axis toward the frame and is adapted to be coupled to the pneumatic air system to supply pressurized air thereto. At least a portion of the axle has a sealed hollow interior forming a pressurized air reservoir and is pneumatically connected to the pneumatic system. According to the invention, the air reservoir is connected to the air spring for pressurizing the air spring.